1. Field of the Invention
The present invention relates to mechanical amplifiers and more particularly to the use of bellows for amplifying a microactuator.
2. Description of the Related Art
The high force capability of electrically induced strain materials such as piezoelectric materials and terfenol-D materials offer high force output with small displacement. Piezoelectric materials are well known in the literature. For example, U.S. Pat. No. 5,595,677, issued to R. R. Neurgaonkar et al., discloses Nb-doped PLZT piezoelectric ceramics.
A relatively new type of electric actuation device, a piezoelectric actuator, has been developed that can potentially replace traditional actuation devices such as solenoid and/or servos. The piezoelectric actuator has several advantages over traditional actuation devices such as lower weight, smaller envelope, high reliability, higher output force, and more precise positioning. However, the piezoelectric actuator does not provide enough displacement to be practical for most applications. Examples of piezoelectric actuators have been disclosed and claimed in, for example, U.S. Pat. No. 5,043,621 and 4,928,030, both issued to G. W. Culp.
Prior attempts to solve the problem of deriving sufficient displacement have included using mechanical levers; belleville washers; metal, plastic or rubber diaphragms; and, hydraulic devices using various sizes of pistons with seals.
U.S. Pat. No. 4,803,393, issued to T. Takahashi, discloses the use of two bellows of different sizes separated by a metallic sleeve. The metallic sleeve includes a filling device for filling and venting and an O-ring for preventing fluid from leaking. The Takahashi device, by virtue of its somewhat complicated design and large number of parts, is not particularly compact. For many applications, such as aerospace applications requiring small, lightweight devices, it would be unworkable.
U.S. Pat. No. 5,055,733, issued to L. Aisleman, discloses a method for converting micromotions into macromotions utilizing telescoping hydraulic actuators of various diameters.
U.S. Pat. No. 4,995,587, issued to R. C. Alexias, discloses an electromechanical motion amplifier for controllably converting an input displacement into an amplified output displacement, using a dual piston arrangement.
U.S. Pat. No. 3,946,551, issued to K. L. Linebrink, et. al., discloses an electromechanical pumping and fuel metering means interfacing an electronic fuel control adapted for small engines.
U.S. Pat. No. 3,501,099, issued to G. M. Benson, discloses a chamber filled with low compressible fluid that is bounded by first and second plungers or diaphragms, the first plunger being operatively connected to the module. The area of the second plunger is established at a size smaller than the first plunger so as to provide for motion amplification of the relatively small mechanical displacement of an electro expansive module.
U.S. Pat. No. 3,766,415, issued to R. E. Dame, et. al, discloses an electro mechanical actuator acting on a large piston to force a small plunger to stroke a larger distance.
U.S. Pat. No. 4,022,166, issued to H. Bart, discloses the use of levers to amplify the stroke of a piezoelectric actuator.
U.S. Pat. No. 4,318,023, issued to C. G. O'Neill, et al., discloses an electro-expansive linear actuator which utilizes a sagittal tension member to amplify linear motion in which the electro expansive member is placed in compression between a fixed base support and a lever support member hingedly connected to the fixed base.
U.S. Pat. No. 5,515,880, issued to J. J. Salas, et. al, discloses a piezoelectric seismic vibrator with hydraulic amplifier in which a dry piston is provided having a cross sectional area which is smaller than the area of a power piston. The pressure within the fluid system acts to amplify the longitudinal displacement of the piezoelectric elements.
The aforementioned devices are generally complex, expensive, bulky and may not be particularly reliable because of their use of multiple parts.